Bisphenols are useful as raw materials of engineering plastics. Polymers using bisphenols are suitable in a wide range of applications such as electronic components, separation films for water treatment, gas separation and hemodialysis etc. However, polyesters having bisphenol repeating units are difficult to dissolve in organic solvents and difficult to mold.
There have thus been developed fluorine-containing polymers using, as monomers, bisphenols or dicarboxylic acids each having a hexafluoroisopropylidene group, i.e., C(CF3)2 in the respective chemical structures for improvement in organic solvent solubility (see Non-Patent Document 1). The thus-obtained fluorine-containing polymers feature good heat resistance, corrosion resistance, water repellency, low water absorption, low dielectric constant, low refractive index and the like.
Further, a fluorocarbinol group is known as a functional group to impart adequate hydrophilicity to fluorine compounds. In particular, a resist resin using a fluorine compound with a 2-hydroxy-1,1,1,3,3,3-hexafluoroisopropyl group, i.e., C(CF3)2OH group (hereinafter sometimes referred to as “HFIP group”) as a raw material shows high transparency and good substrate adhesion when used for lithographic patterning in semiconductor manufacturing processes. When this fluorine compound is used as a resist resin for photolithography, the resist resin shows high sensitivity for exposure to short-wavelength ultraviolet irradiation with the use of an argon fluoride laser (wavelength: 193 nm) etc. as an irradiation source as well as solubility in developers for patterning after the exposure.
As HFIP-containing aromatic polymers, aromatic polyamide or polyimide compounds with HFIP groups have been disclosed (see Patent Documents 1 to 4). It is described in Patent Documents 1 to 4 that the introduction of HFIP groups to aromatic polyamide or polyimide compounds allows improvement in organic solvent solubility and reduction in dielectric constant. It is also described that: in the case of using, as a raw material of HFIP-containing aromatic polyamide or polyimide compounds, a diamine monomer in which HFIP group and amino group are respectively attached to ortho-position carbon atoms, the HFIP-containing aromatic polyamide can be converted to a specific polymer compound of fluorine-containing heterocyclic ring (heteroring) structure by heating and dehydrating the HFIP-containing aromatic polyamide; and this conversion reaction allows further reduction in water absorption and dielectric constant and improvement in heat resistance due to the disappearance of polar hydroxyl groups.
Although the HFIP-containing aromatic polyamide or polyimide compounds have been disclosed as mentioned above, polymers of these aromatic compounds are low in transparency regardless of their high fluorine contents. One reason for such low transparency is that the π conjugated systems of the respective compounds become long in length by the formation of imide rings or heterocyclic rings. Highly transparent materials are usable as not only resist materials but also coatings for flat panel displays, protection films for substrates in electronic circuit boards, protection films for semiconductors and the like.
There is a report about HFIP-containing phenol derivatives (see Non-Patent Document 2) as fluorine-containing compounds in which HFIP groups are added to aromatic polyesters. However, detailed analyses of these compounds, such as identification of the position of substitution of the HFIP groups on the aromatic rings, have not been carried out. Further, there is no report about polymers using fluorine-containing phenolic compounds as fluorine-containing polymerizable monomers. As mentioned above, HFIP-containing aromatic polyesters are expected as polymer materials that combine adequate hydrophilicity with low water adsorption and good transparency of fluorine-containing compounds.
Non-Patent Document 3 discloses the substitution of a hydrogen atom of the HFIP group.